Chemistry World ت

Answers for Prepare for EYE : 5 Questions on Ionic Equations, Colours of Cations & Anions, Acids, Bases, Alkalis, Salts

Thursday, September 22, 2011

Q1 Zinc nitrate reacts with aqueous ammonia (NH4OH) to form a salt and a base. (i) Name the salt and the base. (ii) Describe the observations for the reaction. (iii) Write a chemical equation for the reaction (include state symbols). (iv) Write an ionic equation for the reaction.

(i)The salt formed is Ammonium Nitrate while the base formed is Zinc Hydroxide.

(ii)The alkali and soluble salt are aqueous solutions mixed together.After the reaction,a solid precipitate and an aqueous solution is formed.The solid precipitate is then removed as residue by filtration.When soluble salt reacts with an alkali,it will form a soluble salt and a precipitate.Therefore,when Zinc Nitrate reacts with Aqueous Ammonia,it will form Ammonium Nitrate and Zinc Hydroxide.And the Zinc Hydroxide formed is a white precipitate and it is soluble in excess aqueous ammonia to give a colourless solution.

(iii)Zinc Nitrate + Ammonium Hydroxide = Ammonium Nitrate + Zinc Hydroxide

(iv)

Q2 Ammonium sulfate is heated with sodium hydroxide. (i) Write a chemical equation (include state symbols) for the reaction. (ii) Describe a test for the gas.

(i) Ammonium sulfate + Sodium hydroxide = Sodium sulfate + water + ammonia

(ii)When Ammonium Sulfate is heated with Sodium Hydroxide,it produces ammonia gas.Ammonia gas can be tested by holding a piece of damp red litmus paper over the mouth of a test-tube because the hydroxide ions from ammonia gas will turn the damp red litmus paper to blue.

Q3 An unknown green solution is heated with a piece of aluminium foil and sodium hydroxide solution. (i) The gas produced turns damp red litmus paper blue. Name the gas evolved. (ii) This is a confirmatory test for an anion. Name this anion. (iii) Give a possible cation which gives the green solution.

(i)The gas evolved is Ammonia gas.

(ii)This anion is Nitrate ions.

(iii)This possible cation which gives the green solution is Iron(II) ion.

Q4 Sulfuric acid is titrated with potassium hydroxide in the preparation of potassium sulfate salt. (i) Explain why this method is recommended for the preparation for this salt. (ii) Write an ionic equation for the reaction.

(i)This method is known as titration.It is used because the acid,alkali and the salt are all soluble and colourless solution and this is preparing a Group (I) salt.Hence,we need titration method with an indicator to determine the end-point of the neutralisation between the acid and alkali,before we prepare the salt.

(ii)Sulfuric Acid + Potassium Hydroxide = Potassium Sulfate + Water

Q5 Excess zinc carbonate is added to hydrochloric acid in the preparation of zinc chloride salt. (i) Write an ionic equation for the reaction. (ii) Why excess zinc carbonate is used? (iii) Briefly explain how the zinc chloride crystals can be obtained.

(i)

(ii)Excess zinc carbonate is used to ensure that all the hydrochloric acid is completely reacted.When there are excess white zinc carbonate seen,the reaction has stopped.

(iii)To obtain zinc chloride crystals,the steps are as follows:

Step 1:Add excess zinc carbonate solid to a beaker of dilute hydrochloric acid until there is excess white zinc carbonate solid left behind.

Step 2:Filter to remove the excess unreacted zinc carbonate solid.

Step 3:Evaporate the zinc chloride solution to remove the water and make a saturated solution.

Step 4:The hot saturated solution form zinc chloride crystals when it is cooled.

This method is used to prepare soluble but not Group (I) salts.Excess zinc carbonate will ensure that all the hydrochloric acid is completely reacted.When there is excess white zinc carbonate seen,the reaction has stopped.Filter the mixture is to remove the excess unreacted zinc carbonate.Later the filtrate is evaporated to remove most of the water so that it becomes saturated.On cooling,the saturated zinc chloride will form crystals.Do not directly heat the crystals as it will remove water of crystallisation.

writtern @2:16 AM

Comments for classmates

Tuesday, July 5, 2011

These are some of the comments for my friend's answers:

Number 05:Shin Yoong

Shin Yoong's answer is very clear and detailed.Her drawing on the atoms and ions is very easy to understand and neat.Her blogskin is very nice.She put in effort to decorate her blog and make her blog as lively as possible.Great work! :)

Number 12:Shu Yu

Shu Yu's answer is very detailed and infomative.Her drawing is very clear.And i can see that she put in a lot of effort in making her blog a nice and outstanding one.She make the effort to do some research on the atoms and she even write down the atomic mass and nucleon number for the sulfur and sodium which is excellent.Excellent work! :)

Number 16:Wan Ling

Wan Ling's answers are very detailed,clear and easy to understand.Her blog is very nice and well-decorated.She put in a lot of effort to do the assignment and she even do research for the images of some atoms and ions which is very well-done.She also find out the average for the chlorine and use it as a form of explanation for the isotopes.Very good Work! :)

writtern @2:35 AM

Atomic Structure Assignment(Chemistry Assignment 1)

Friday, July 1, 2011

1. What does an atom looks like? What are the sub-atomic particles inside it.....(talk about electrons, neutrons, protons, electron shells, nucleus....)
-Matter is built up from small individual particles called atoms.Atoms are the basic building blocks of matter.An atom is made up three different types of sub-atomic particles,they are the protons,neutrons and electrons.The proton(represented by the symbol,p) has a relative mass of 1 and a relative charge of +1.The neutron(represented by the symbol,n) has a relative mass of 1 and a relative charge of 0.The electron(represented by the symbol,e) has a relative mass of 1/1840 and a relative charge of -1.The protons and neutrons are found in the nucleus of the atom.These two particles that made up the nucleus are known as nucleons.The protons and neutrons make up the dense core of the atom.The electrons move around the nucleus in definite energy levels or electron shells.The first electron shell can hold up to 2 electrons while the second and third shell can hold up to 8 electrons.The composition of protons,neutrons and electrons in an atom can be determined from its proton number and nucleon number.The proton number is the number of protons in an atom while the nucleon number is the total number of protons and neutrons in an atom(number of protons+number of neutrons=nucleon number).Since an atom is electrically neutral,the number of protons is the same as the number of electrons.The number of neutrons is found by using the nucleon number to subtract away the proton number.

2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
-A sodium atom has a proton number of 11.Since sodium is in Group (I),it is a metal.Metals have to lose electrons in order to achieve stability(stable noble gas configuration).Therefore,metals lose electrons to form a cation(positive ion).In the case of sodium,it has an electronic configuration of 2.8.1,since it has 1 valence electron in the outermost shell,it gives away this electron to become a cation and achieve a stable noble gas configuration of 2.8.When it loses electrons,it became a sodium ion.This is why i drew it this way.

sodium atom: sodium ion:

3. Draw the atomic structure of a sulfur atom and a sulfide ion....explain why you draw it this way.

-A sulfur atom has a proton number of 16.Since sodium is in Group (VI),it is a non-metal.Non-metals have to gain electrons in order to achieve stability(stable noble gas configuration).Therefore,non-metals gain electrons to form an anion(negative ion).In the case of sulfur,it has an electronic configuration of 2.8.6,since it has 6 valence electron in the outermost shell,it gain two more electrons to become an anion and achieve a stable noble gas configuration of 2.8.8.When it gain electrons,it became a sulfur ion.This is why i drew it this way.

sulfur atom: sulfide ion:

4. Chlorine-35 atom and Chlorine-37 atom are called isotopes...Use these two examples to explain what is 'isotopes'.
-Isotopes are different atoms of the same element which have the same number of protons but different number of neutrons.Isotopes of the same element have a similar chemical properties but different physical properties.The chemical properties of isotopes are similar because chemical reactions involve only the electrons and not the protons and neutrons and they have the same number of valence electrons for bonding.The physical properties differ because the relative masses of the isotopes differ.There are two different types of isotopes,radioactive isotopes and non-radioactive isotopes.The example of isotopes are in Chlorine-35,there are 17 protons and 18 neutrons.In Chlorine-37,there are 17 protons and 20 neutrons.Since there are same number of protons but different number of neutrons,we can conclude that Chlorine-35 and Chlorine-37 are isotopes.And the average mass number of Chlorine-35 and Chlorine-37 is 35.5.

Chlorine-35 atom:

Chlorine-37 atom:

5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??

-Sodium is a metal because it loses electron to complete the valence shell and become positively charged ions(cations) and it is in group (I) while Sulfur is a non-metal because it gains electrons to complete the valence shell and become negatively charged ions(anions) and it is in group (VI).According to the periodic table,metals are those elements that are in group (I) and (II) and non-metals are those elements that are in group (III),group (IV),group(V),group(VI),group (VII) and group (0).In between group(II) and group (III),there are metals called the transition metals,these metals(elements) are usually coloured.